Cancer is prevalent: there were about 3.2 million cancer cases diagnosed (53% men, 47% women) and 1.7 million deaths from cancer (56% men, 44% women) in Europe (Ferlay et al. (2007) Ann. Oncol. 18(3):581-92). In the United States, the probability of developing invasive cancer is 38% for females and 46% for males that live to be 70 years old and older. In the US about 1.4 million new cases of cancer are expected for 2006. Although the five year survival rate for cancer is now 65%, up from about 50% in the mid-nineteen seventies, cancer is deadly. It was estimated that 565,000 people in the United States would die from cancer in 2006 (American Cancer Society, Surveillance Research, 2006). Despite tremendous advances in cancer treatment and diagnosis, cancer remains a major public health concern. Accordingly, there is a need for new therapeutics with activity in cancer.
Another health crisis is facing industrialized nations. As the population in these countries age, neurodegenerative diseases are affecting more and more people, posing a tremendous economic burden to national health systems. Alzheimer's disease is the largest neurodegenerative disease; disease modifying drugs have long been sought, but to-date, none have been identified. Other neurodegenerative conditions include Parkinson's disease, Huntington's disease, Lewy Body dementia, and which are all characterized by disease progression which robs the patients of their ability to perform normal daily activities, eventually leading to death.
One similar characteristic amongst many cancers and neurodegenerative diseases is aberrant gene expression. A number of compounds have been shown to alter gene expression, including histone deacetylase inhibitors which alter the histone acetylation profile of chromatin. Histone deacetylase inhibitors like SAHA, TSA, and many others have been shown to alter gene expression in various in vitro and in vivo animal models. Another modification that is involved in regulating gene expression is histone methylation. Histones can be subject to numerous modifications including lysine and arginine methylation. The methylation status of histone lysines has recently been shown to be important in dynamically regulating gene expression.
A group of enzymes known as histone lysine methyl transferases and histone lysine demethylases are involved histone lysine modifications. One particular human histone lysine demethylase enzyme called Lysine Specific Demethylase-1 (LSD1) was recently discovered (Shi et al. (2004) Cell 119:941) to be involved in this crucial histone modification. Inactivation of LSD1 in Drosophila (dLSD1) strongly affects the global level of mono and dimethyl-H3-K4 methylation but not methyl-H3K9 while the levels of some other histone methylation and acetylation marks remained the same. LSD1 inactivation resulted in elevated expression of a subset of genes, including neuronal genes in non-neuronal cells analogous to the functions of LSD1 in human cells. In Drosophila, dLSD1 is not an essential gene, but animal viability is strongly reduced in mutant animals in a gender specific manner (Destefano et al. (2007) Curr. Biol. 17(9):808-12). Mouse homozygous LSD1 knock-outs were embryonic lethal.
LSD1 has a fair degree of structural similarity, and amino acid identity/homology to polyamine oxidases and monoamine oxidases, all of which (i.e., MAO-A, MAO-B and LSD1) are flavin dependent amine oxidases which catalyze the oxidation of nitrogen-hydrogen bonds and/or nitrogen carbon bonds. Recent experiments with LSD1 have shown that it is involved in diverse process such as carcinogenesis (Kahl et al. (2006) Cancer Res. 66:1341-11347) and vascular inflammation (Reddy et al. (2008) Circ. Res. 103:615). It was found that a commercially available antidepressant, Parnate®, which targets monoamine oxidase (MAO), also inhibits LSD1 at clinically relevant concentrations (Lee et al. (2006) Chem. Biol. 13:563-567). Schmidt et al. found “IC50 values for 2-PCPA of 20.7±2.1 μM for LSD1, 2.3±0.2 μM for MAO A, and 0.95±0.07 μM for MAO B.” See Schmidt et al. (2007) Biochemistry 46(14)4408-4416. Thus, Parnate (2-PCPA) is a better inhibitor of MAO-A and MAO-B as compared to LSD1. Schmidt et al. note that the IC50 values for irreversible inhibitors of LSD1 like parnate can greatly depend on assay conditions. Additionally, derivatives of Parnate also can inhibit LSD1 (Gooden et al. (2008) Bioorg. Med. Chem. Let. 18:3047-3051). Another class of compounds was recently disclosed to inhibit LSD1 activity: polyamines (Huang et al. (2007) PNAS 104:8023-8028). These polyamines inhibit LSD1 modestly and were shown to cause the re-expression of genes aberrantly silenced in cancer cells.
LSD1 is also involved in regulating the methylation of lysines of some proteins which are not histones, like P53 and DNMT1 which both have critical roles in cancer.
Lee et al. ((2006) Chem. Biol. 13:563-567) reported that tranylcypromine inhibits histone H3K4 demethylation and can derepress Egr1 gene expression in some cancer lines. A body of evidence is accumulating that Egr-1 is a tumor suppressor gene in many contexts. Calogero et al. ((2004) Cancer Cell International 4:1) reported that Egr-1 is downregulated in brain cancers and exogenous expression of Egr-1 resulted in growth arrest and eventual cell death in primary cancer cell lines. Lucerna et al. ((2006) Cancer Research 66, 6708-6713) showed that sustained expression of Egr-1 causes antiangiogenic effects and inhibits tumor growth in some models. Ferraro et al. ((2005) J. Clin. Oncol. March 20; 23(9):1921-6) reported that Egr-1 is downregulated in lung cancer patients with a higher risk of recurrence and may be more resistant to therapy. Scoumanne et al. ((2007) J Biol Chem. May 25; 282(21):15471-5) observed that LSD1 is required for cell proliferation. They found that deficiency in LSD1 leads to a partial cell cycle arrest in G2/M and sensitizes cells to growth suppression induced by DNA damage. Kahl et al. ((2006) Cancer Res. 66(23):11341-7) found that LSD1 expression is correlated with prostate cancer aggressiveness. Metzger et al. ((2005) Nature 15:437(7057):436-9) reported that LSD1 modulation by siRNA and pargyline regulates androgen receptor (AR) and may have therapeutic potential in cancers where AR plays a role, like prostate, testis, and brain cancers. Thus, a body of evidence has implicated LSD1 in a number of cancers, which suggests that LSD1 is a therapeutic target for cancer.
The phenylcyclopropylamines have been the subject of many studies designed to elucidate a SAR for MAO inhibition. Kaiser et al. ((1962) J. Med. Chem. 5:1243-1265); Zirkle et al. ((1962) J. Med. Chem. 1265-1284; U.S. Pat. Nos. 3,365,458; 3,471,522; 3,532,749) have disclosed the synthesis and activity of a number of phenylcyclopropylamine related compounds. Zirkle et al. ((1962) J. Med. Chem. 1265-1284) reported that mono- and disubstitution of the amino group of trans-2-phenylcyclopropylamine with methyl decreases the activity only slightly whereas monosubstitution with larger groups like alkyl and aralkyl groups results in considerable loss of activity in the tryptamine potentiation assay for MAO activity. Studies have also been conducted with phenylcyclopropylamine related compounds to determine selectivity for MAO-A versus MAO-B since MAO-A inhibitors can cause dangerous side-effects (see e.g., Yoshida et al. (2004) Bioorg. Med Chem. 12(10):2645-2652; Hruschka et al. (2008) Biorg Med Chem. (16):7148-7166; Folks et al. (1983) J. Clin. Psychopharmacol. (3)249; and Youdim et al. (1983) Mod. Probl. Pharmacopsychiatry (19):63). Other phenylcyclopropylamine type compounds are disclosed in Bolesov et al. ((1974) Zhurnal Organicheskoi Khimii 10:8 1661-1669) and Russian. Patent No. 230169 (19681030). Gooden et al. ((2008) Bioorg. Med. Chem. Let. 18:3047-3051) describe the synthesis of phenylcyclopropylamines derivatives and analogs as well as their activity against MAO-A, MAO-B, and LSD1. None of the compound made in Gooden et al. showed a lower Ki for LSD1 as compared to either MAO A or MAO B. Additionally, most of the Gooden et al. phenylcyclopropylamine derivatives were better inhibitors of MAO-A as compared to MAO-B.
In view of the lack of adequate treatments for conditions such as cancer, there is a desperate need for disease modifying drugs and drugs that work by inhibiting novel targets. There is a need for the development of LSD1 selective inhibitors particularly those which selectively inhibit LSD1.